P0455 P0xxx · Powertrain (P) Low severity
Evaporative Emission Control System Leak Detected (Gross Leak)
A large leak — the system cannot hold any pressure at all. Usually an obvious physical fault: missing cap, split hose, or a disconnected line.
Severity guidance: Low — usually no drivability impact, fix at the next service
Symptoms you will notice
- Strong fuel smell
- Check-engine light
- Visible fuel vapour in extreme cases
Common causes
Ordered from most to least likely — start at the top.
- 1 Missing or badly seated fuel cap
- 2 Disconnected vapour hose
- 3 Split filler neck hose
- 4 Damaged canister
How to diagnose it
Cheapest and least invasive first — most of these codes are not a parts problem.
- ✓ Look for the cap first — the majority of gross leaks are nothing more than that.
- ✓ Follow every vapour hose from tank to canister to purge valve.
- ✓ Smoke-test to confirm the repair.
- ✓ Re-run the EVAP monitor with a scan tool before returning the car.
Repair options
- Fit the correct fuel cap
- Reconnect or replace the hose
- Replace the damaged canister
P0455 — frequently asked questions
Is it an emergency? +
No, but a gross leak is a genuine fire risk. Do not park over a heat source and fix it promptly.
Will the light clear on its own? +
Only after the monitor runs and passes, which needs a drive cycle with a partly filled tank.
Confirm the diagnosis before you buy parts
Send us the code, freeze-frame data and the vehicle — our engineers will tell you what to test first.